Combustion control system



Sept. 1, i936n s, BRISTOL COMBUSTION CONTROL SYSTEM .File Aug. 9, 1934 3 sheets-sheet 1 si N INVENTOR. EDWARD 5. 52mm.

ATTORNEY.

Sept. 1, 1936. E. s. BRISTOL COMBUSTION CONTROL SYSTEM Filed Aug. 9, 1954 3 Sheets-Sheet 2 Mci A TTORNEY.

' SePtl, 1935- E. s. BRISTOL 2,053,061

COMBUSTION CONTROL SYSTEM Filed Aug. 9, 1934 3 Sheets-Sheet 3 INI/ENTOR. EDWARD 5. BRISTOL Maz/.Cm

u ATTORNEY.

Patented Sept. 1, 1936 PATENT GFFICE COMBUSTION CONTROL SYSTEM Edward S. Bristol, Philadelphia, Pa., assignor to Leeds & Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania Application August 9, 1934, Serial No. 739,123

32 Claims. (Cl. 290-2) My invention relates to new and improved combustion control systems and more particularly to such systems suitable for application to the control of fluid-driven prime mover systems including electric generating apparatus.

While my invention is of general application, it is particularly useful in systems including boilers having small thermal storage capacities, for example, those of the type known in the art as flash tube boilers. In this type of apparatus it is desirable to maintain a close correspondence between the factors entering into the production of the motive ud, for example, fuel, air, and water or other fluid, vin spite of variations in load upon the system within a wide range. For instance, with a limited water storage capacity, it is obvious that the rate of supply of feed water to the boiler must be closely correlated with the rate of combustion in order to prevent an excessive rise insteam temperature or pressure occasioned by a deficiency of water, or, on the other hand, an excessive lowering of steam temperature or pressure by an excess of water.

A combustion control system embodying my in- 23 vention is illustrated as applied to a fluid-driven prime system comprising a fluid-driven prime mover, a boiler for supplying motivefluid thereto, and an electric generator driven by the prime mover. My combustion control system includes means for establishing a master control force, preferably an electric current, varied primarily in accordance with the frequency of the current generated by the system and, secondarily, in accordance with the electrical power output of the generator, as compared with the power output of one or more other'generators included in the same or connected systems. The ,primary control may be relatively quick-acting, rapidly to correct any deviations in frequency of the system 40 from normal, while the secondary control may be relatively slow-acting and effective tol prevent a gradual or continuous shifting of the system load between the several generators connected thereto. As an alternative, the primary control may be in response to the load on the system which may be correlated with any desired regulating or controlling force.

The master control current thus established may be employed to control one or more of the following factors of combustion or other operatact as a check upon the correspondence in the rate of combustion and the rate of supply of l water, and/or by a device responsive to the temperature of the water within the ash tube of the boiler; the flow of furnace gases. As an addition or alternative, the fiow of furnace gases may be controlled by a device responsive to the pressure within the combustion chamber to maintain such pressure substantially constant, either by controlling the stack damper or the speed of a motor driving a forced draft fan. In case the system includes a prime mover supplied by two or more boilers, the master control current may be divided and adjusted either manually or automatically in proportion to the loads which it is desired the several boilers shall carry, and the branch currents then employed to regulate the control factors of the several boilers.

In each case the factor controlled, such, for

. example, as the supply of air, fuel, motive fluid or the like, is preferably metered; that is, it is employed tov produce a control effect whichis a measure of the factor and is compared with the master control current or other control means to 'produce an exact correspondence between the several operating factors of the system under each condition of load on the system, thus insuring optimum operating conditions. Such an arrangement is to be contrasted with a system in which the various controlling devices are varied proportionally and in which the non-linear characteristics of the several controlling devices or the non-linear relations between the several oontem embodying my invention; while Fig. 1a is a detail diagram of a portion f the control circuit of Fig. 1; n

Fig. 211s a similar diagram in which a master control current influences different control y:factors of the system; while Fig. 2a illustrates a further control feature which may be added to the system of Fig. 2;

Fig. 3 is a wiring diagram of a modified arrangement for regulating the master control current.

Referring now more particularly to Fig. 1 of the drawings, there is shown a generating system including my improved combustion control -system and comprising a pair of units A and B connected to supply alternating current to a common load circuit I0. 'I'he unit A consists of an alternating current generator II driven by a suitable prime mover, such as a. steam vturbine I2, to which motive uid is supplied by a pair of boilers I3 and I4. Similarly, the unit B comprises a pair of alternating current generators I5 and I1 driven by the turbines I6 and I8, respectively, supplied with motive uid from a single boiler I9. While the boilers I3, I4 and I9 may be of any desired type, my invention is particularly suitable for use in systems embodying boilers having a relatively lowthermal storage capacity, known in the art as ash boilers.

In order to control the several factors enter-y ing into the production of motive fluid and its supply to the prime movers I2, I6 and I8, there is established a master control current foreach of the units A and B. These control currents may be supplied from a suitable source of control power, such as a direct current circuit 20. The master control currents areestablished in control circuits 2I and 22 individual to the units A and B, respectively, while the control circuit 2I is, in turn, divided into circuits 23 and 24 individual to the boilers I3 and I4, respectively. The master control currents owing in the circuits 2l and 22 are regulated to control the various factors of combustion and supply of motive uid, as described more fully hereinafter, by means of a pair Ain the circuits are measures of the load on the several boilers, as explained more fully hereinafter.

The master control currents owing inthe circuits 2I` and 22 may be regulated by any suitable operating conditions of the system. In the arf rangement of Fig. 1, they are regulated primarily in responseto the frequency of the alternating current of the system supplied by generators II, I5, and I 1 to maintain this frequency substantially constant., To this end, there is provided a irequency-responsive network 29 one diagonal of which is connected to the alternating current circuit I0, while the other includes a contactmaking instrument or galvanometer 30 provided with contacts 30a connected to control the motors 25a and 26a of the adjustable resistances 25 and 26, respectively, as indicated schematically by the dotted lines. This conventional interconnection between the controlling and controlled devices has been adopted throughout the drawings' to avoid excessive complexity, as the particular controlling .and controlled devices, perse, form no part of my invention. The frequency-responsive bridge 29, together with the contactmaking instrument 30,.rnay be of any of the several types well-known in the art, although I prefer to use a self-balancing bridge and contact structure, described in Wunsch Patent No. 1,751,538.

In addition, the master control currents may be subjected to a secondary regulation in response to the division of the system load between the several generators II, I5, and I1. There is illustrated in Fig.` 1 an arrangement for mainr to the generator I5 and adjusts a potentiometer' 34 consisting of similarelements, and a contact making wattmeter 35 is connected in the leads of the generator I1 and operative to adjust a potentiometer 36. The electromotive force derived f from the potentiometer 32 is balanced against the sum of the electromotive forces of the potentiometers 34 and 36, and contact making instruments 31 and 38 are included in this balancing circuit individual to 'the units A and B, respectively. This balancing circuit may be traced from the potentiometer impedance 32a, conductor 39, potentiometer impedances 34a' and 36a, conductor 4I, instruments 38 and 31 and conductor 42. The instruments 31 and 38 may be of any suitable type of contact making ammeters or galvanometers,-but are preferably of the type disclosed in Fig. 6 of Doyle Patent No. 1,918,021. By a proper proportioning of the circuit constants of the potentiometers 32, 34 and 36, any desired load distribution between the generator II and the generators I5 and I1 may be maintained.

The manner in which the primary and secondary control of the rheostats 25 and 26 is obtained will be clear from Fig. 1a of the drawings, in which the contacts 30a and 31a are those of the frequency-responsive instrument 30 and the load ratio responsive instrument'31, respectively. The motor 25a is provided with a pair of elds 25o and 25dl of opposite polarity connected to be selectively energized from va suitable source tudes, as determined by the calibration of. the or 31a, or both. Included in the circuit oi! the contacts 30a are a pair of relatively low resistance devices 43a and 43b, while a pair of relatively highresistance elements 44a and 44h are connected in series with the contacts 31a. By means yo1 such an expedient, if the instruments 30 and 31 operate'in the same sense, one of the elds 25e and 25d is energized through a pair of resistors, for example, 43a and 44a, in parallel,

so that theenergization of the motor 25a is a maximum, and it will rotate at a maximum speedin the particular direction. In case either of the instruments 30 or 31 alone operates its contacts, the motor 25a will rotate at. correspondingly reduced speed. In case the instruments 30 and 31 operate in an opposite sense, the elds 25e and v25d will be diierentially energized, but the mothe generators I5 and I1 may be maintained by means of .additional potentiometers 45 and 46 also adjusted by means of the contact making wattmeters 33 and `35, respectively. 'I'he poten" tiometers 45 and 46 are included in a balancing circuit in which is connected a contact making 2,053,031 'instrument 41, the contacts 41a of which control a motor-operated valve mechanism 46 which adjusts valves 49 and 50 in the fluid conduits 5| and 52, respectively, in opposite senses to vary the distribution of motive fluid to the prime movers I6 and I8.

In case it is desired to change the primary regulation of the master control currents from the frequency-responsive network 29 to apparatus for maintaining constant load on the system, there is provided a switch 53 which, when operated into its lower position, connects the conductors 39 and 42 across a potentiometer 54 energized from a battery 55. In this case, a switch 56, included in the connections to the frequency-responsive network 29, is operated to open circuit position. Again, in case it is desired to control the output of the system from 'a remote point, either to maintain the output constant-or to maintain a predetermined ratio between the output of the system and that of another connected or independent system, the switch 53 may be operated to its upper position, in which it connects the conductors 49 and 42 to the conductors 51 extending to the point of remote control.

In order to facilitate invention, the operation of the above described apparatus for regulating the master control currents of the two units will be explained before coming to the description of the apparatus by means of which the control currents effect the desired regulation of conditions of combustion in the boilers. Assume, for example, that the switch 53 is in the open position illustrated, that the load on the system suddenly increases and that the characteristics of the generators II, I5, and I1 have a certain dissimilarity which causes the generator |I to assume a greater proportion of the increase in the load than the generators I and I1. Because of change of frequency due to the sudden increase of load, the frequencyresponsive network 29 will become unbalanced and the instrument 39 will close one of its contacts 30a to energize the motors 25a and 26a of the control rheostats 25 and 26, respectively. At the same time, the wattmeter 3| will adjust the setting of the potentiometer 32, and the wattmeters 33 and 35 will adjust the settings of the potentiometers 34 and 36, respectively, but the setting of the potentiometer 32 will be such that the electromotive force impressed upon the conductors 39 and 42 of the balancing circuit will,

be greater than the sum of the electromotive forces from the potentiometers 34 and 36, with the result that the'instruments 31 and 38 become unbalanced to control their respective control rheostats in opposite senses. The instrument 31 will close one of its contacts 31a corresponding to that one of the contacts 30a closed by the instrument 30, for example, the left-hand contacts (Fig. 1a), to place the resistors43a and 44a in parallel in the energizing circuit of the motor 25a. IThe motor 25a now operates at its vmaximum speed to adjust the control current flowing in the circuit 2| which, as described hereinafter, is effective to change the conditions of combustion by a proportionate amount and to increase the input of motive fluid to the prime mover I2 to correspond to the increase in load on the system.

At the same time, the instrument 33 will close its opposite contacts, for example, its right-hand an understanding of my motive force obtaining contacts, so that the two elds of the motor 26a are differentially energized and the resultant field is suiicient to rotate the motor at only a very slow speed, if at all. Inbrief, the control current of unit A is increased very much more rapidly than the control current of the unit B to increase the power input to the generator II and bring the frequency of the system back to normal and, at the same time, to restore the division of load between the units A and B to its proper value.

In case the units A and B should assume the increase in load in the proper proportion, obviously the circuit including the potentiometers 32, 34v

and 36 will remain in balance and the frequencyresponsive network 29 will control the rheostats 25 and 26 similarly and to like extent. Again, in case the load on the system as a whole remains unchanged but the distribution between the units A and B changes for any cause, the frequency-responsive network will remain in balance, while the load distribution circuit, including potentiometers 32, 34, and 36 will become unbalanced to operate the instruments 31 and 38 in opposite senses. These instruments, in turn, energize the motor control rheostats 25 and 26 in opposite directions and to a similar extent, thus restoring the balance by the proper change in the control currents of the two units.

In case it is desired to control the power outputs of the units lA and B to maintain a predetermined and adjustable load thereon, the switch 56 is opened, disconnecting the frequency-responsive network 29, while the switch 53 is operated to its downward position, connecting a portion of the potentiometer 54 between the conductors 39 and 42. The electromotive forces of the potentiometers 32, 34 and 36 are now compared with the constant, but adjustable electromotive force of the potentiometer 54 and the instruments 31 and 38 are operative to regulate the control currents in the circuits through the rheostats 25 and 26, respectively, to maintain the power outputs of the generator I| and the generators I5 and I1 at constant magnitudes, as determined by the calibration of the potentiometers.

Similarly, in case it is desired to control the outputs of the several generators from a remote point, either to maintain them at a constant adjustable value, or a value dependent upon the load on other units or systems, or other variable conditions or factors, the switch 53 is operated to its upper position in which the conductors 39 and 42 of the balancing circuit are connected to the conductors 51 extending to the point of remote control. An electromotive force representative of the controlling condition is mpressed upon the conductors 51 at this remote point and the balancing circuit, including potentiometers 32, 34, and 36 and instruments 31 and 38 will operate to maintain the power output of the generators II, I5, and I1 corresponding to the particularvalue of the controlling electroat any\given time.

In the system illustrated, the generators I5 and I1 are supplied by a common boiler I 9 so that it is not possible to control the distribution of load therebetween by controlling vthe conditions of combustion in the boiler. Such control may be effected, however, by an auxiliary balancing circuit comprising a potentiometer 45 controlled also by the wattmeter 33 and a potentiometer 46 controlled by the wattmeter 35. The

proper division of load'between the generators` I5 and I-1, to operate the motor-driven mechanism 48 to adjust the settings of the valves 49 and 50 in motive fluid conduits 5I and 52, respectively, to the prime movers I6 and I8.

The apparatus, by means of which the control currents, established as described above, regulate the conditions of combustion in the boilers of the units A and B, will be considered by reference to a, particular boiler, for example, boiler I3. The po-rtion of the master control current owing in thel circuit 23 regulates or controls devices for supplying fuel, air and motive iiuid, such as water, to the boiler. The apparatus for controlling the supply of fuel to the boiler comprises a fuel-feeding device 60 driven by a motor 6I, the fuel being delivered to a pulverizer 62 driven by a motor 63 and the pulverized fuel,

together with a current of air, passing through a conduit 64 and into the combustion chamber of boiler I3. The motor 6I supplying the fuel to the boiler drives, also, an auxiliary tachometer generator 65, the electromotive force of which is balanced against that of a potentiometer 66 included in series with the master control circuit 23 which electromotive force is, of course, proportional to the control current. The balancing circuit includes a contact making instrument 61, the contacts of which control a motor operated rheostat in circuit with the fuel feed motor 6I.- The speed of the motor 6I, and thus the electromotive force of the tachometer, 65, is a directy measure of the fuel supplied to the boiler. By balancing this electromotive force against an electromotive force proportional to the master control current, it will be seen that the rate offuel supplied is, at all times, proportional to the master control current. This balance is maintained by the instrument 61 which adjusts the speed of the motor 6I through the rheostat 68 to the proper value for maintaining the balance.

The air for supporting combustion is supplied to the combustion chamber of boiler I3 by means of a blower or fan 69 driven by a suitable motor 10. A device for producing a differential pressure dependent upon the rate of air supplied to the boiler, such as an orifice 1I, is interposed between the fan 69 and the boiler. This diierential pressure is applied to a. bell-type manometer 12 of the controller-C, the` unbalanced moment of which is balanced by a current balance 13 provided with contacts 14 controlling a motor-operated rheostat 15 in circuit with the motor 10. As is` well understood by those skilled in the art, the differential pressure acting upon the of the motor 10 to that value for which the fan 69 supplies the proper amount of air for 'a given value of the master control current. The motiye uid, such as water, is supplied to the boiler by means of a feed-water pump 16 driven by, a motor 11. A differential pressureof .the controller C".

creating device, such as an oriiice 18, is interposed between the pump 16 and the boiler I3, and the differential pressure thereacross is connected to the armsof a tilting manometer 12' of a controller C which is similar to the controller C, except that the manometer 12 is adapted to respond to differences in liquid pressure, rather than gaseous pressure.

The master control current flows also through the current balance 13 of the controller C' and, as in the case of the controller C, operates through a motor-driven rheostat 19v in the circuit of themotor 11 to maintain a linear relationship between the master control current and the rate of flow of motive'iiuid to the boiler I3.

to by-pass a variable portion of the master control current therefrom. A thermocouple 8I is included in the outlet conduit of the boiler and is connected in circuit with an adjustable potentiometer 82 through a contact making instrument 83, the contacts 84 of which control the motorvbelow a desired value, the ratio between the master control current and the rate of flow of feed water is changed to decrease the supply of feed Water.

In certain cases, also, it is desirable to maintain the pressure within the combustion chamber of the boiler substantially constant, irrespective of variations in operating conditions, particularly variations in thesupply of air to support combustion. This may be accomplished by'means of a damper 85 located in the stack or flue of the boiler, the position of which is adjusted by means of a motor 86 through a suitable operating mechanism 81. The motor 86 is controlled by a. controller C" which is similar to the controllerC except that it is provided with only a single pressure bell which is balanced against a Weight 88 and a spring 88 rather than against a current balance. The pressure bell 12" of the controller C is connected by means of a conduit 8'9 to the Acombustion chamber of the boiler and is thus subjected directly to the pressure therein. The contacts 14 of. the controller C" control the motor 86 to adjust the setting of the damper 85 to maintain the pressure in the combustion chamber at a, predetermined value corresponding to balance While separate sources of current are shown for the several motors controlling the supply of the several factors of combustion, for the sake of clarity, it will be apparent that these motors may be energized from any suitable source of direct or alternating current.

From the foregoing discussion, the cooperation of the several control devices for governing conditions of combustion inthe boiler I3 will be readily understood. In brief,a linear relationship is established between the master control current and the rate of supply of fuel to the boiler; between this current and the rate of supply of air tothe boiler; and between this current and the rate of supply of feed water. By this means, the several factors entering into the operation of the boiler are controlled and varied rapidly and proportionately to maintain optimum conditions of combustion and generation of steam. The proportionality is maintained to a high degree of accuracy, since, in the control of each of these factors, the control current is balanced against an effect which is a direct measure of the factor, as contrasted with certain arrangements 'of th'e prior art in which the controlling force acts upon a number of control devices which are solely motive devices and which may have widely dissimilar control characteristics. In addition, in order to secure optimum conditions of combustion and generation of steam, the ratio of the master control current to the rate of supplylof feed water is modified to maintainthe temperature of the generated steam within predetermined limits and the pressure obtaining in the combustion chamber of the boiler is maintained at a substantially constant magnitude.

The control devices for regulating the conditions of combustion in the boiler I4 are, in all respects, similar to those of the boiler I3 with the exception of the device C controlling the rate of supply of fuel to the boiler and, with this exception, are illustrated schematically in order to simplify the drawing. The apparatus for controlling the supply of fuel to the boiler, in this case, is suitable for the control of fluid fuel, such as gas, oil or the like, and comprises a valve 90 included in the fuel inlet to the boiler, the position of which is adjusted by a motor 9| through a suitable mechanism Sia. The mechanism 9| a also adjusts the setting of a potentiometer 92 supplied from a suitable source, such as a battery 93, the adjustable contact of the potentiometer 93 being mechanically interconnected with the operating arm of the valve 90. The potentiometer 92 is connected in a balancing circuit including the resistance 66 traversed by the master control current in the circuit 24 and a contact making instrument 61, the contacts 61a. of which control the motor 9|. In the operation of this control apparatus, in case the electromotive force l derived from the potentiometer 66 differs from that derived from the potentiometer 92, the instrument 61 will indicate an unbalance and operate its contacts 61 to energize the motor 9 I, which varies the setting of the potentiometer 92 to restore the balance. The motor 9| coincidentally changes the setting of the valve 90 and the calibration of the mechanism is such that the rate of flow of fluid through the valve 90 Varies linearly with the master control current in the circuit 24. In other respects, the operation of the combustion control apparatus of the boiler I4 is similar to that described above.

Again, the combustion control apparatus associated with the boiler I9 is similar to that of the boiler I4 with the exception that the motor-operated valve 90-9I is controlled by a controller C identical to the controller C associated with the boiler I3. The manner in which it maintains a linear relationship between the master control current flowing in the circuit 22 and the rate of iiow of fuel through the valve 9i! is identical to that described above in connection with the boiler I3 in which a linear relation is maintained be- Ltween the master control current in the circuit 23 and the rate of supply of feed water.

In Fig. 2 is shown a system in which the master control current, established as in arrangement of 'nected across the orifice 18 in the inlet to the feed water to the boiler. The device C', responsive to the rate of flow of feed water, is connected to control the motor-operated rheostat 25 jointly with the load-ratio instrument 31, as in the arrangement of Fig. la, and thus serves to balance this rate against the master control current.

This may be termed the secondary control. The master control current as thus established flows through the potentiometer 66 which cooperates with a vpotentiometer 92 and the indicating instrument 61 to adjust the valve 90 in the conduit supplying fluid fuel to the boiler, to maintain a linear relation between the control current and the rate of supply of fuel to the furnace, as in the control of the boiler I4.

In the system of Fig. 2, a modified control apparatus is utilized to maintain a correct ow of gases through the furnace and a correct furnace pressure. This apparatus comprises a control device C connected to spaced points of the combustion chamber of the furnace through conduits 89 and thus responsive to the rate of flow of the combustion gases through the boiler. The differential pressure between these points is balanced against the control current which ows through the current balance 13 of the device C. The contacts 14 of this device control a motor 86', which determines the setting of a damper 85 interposed between the forced draft fan 69 and the furnace, and varies the setting of the damper 85 through the motor-operated mechanism 86--81 to maintain the flow of combustion gases proportional to the master control current.

This control of the vrate of air flow may be modified to maintain the pressure within the combustion chamber substantially constant by means of the control device C" connected to the combustion chamber through the conduit 89. The pressure existing at this point is balanced against the weight 88 and spring 88' and the contacts 14 of the device C" control the motor operated damper 8586' in the air inlet to the boiler jointly with the controller C. The control of the motor-operated damper 85-86 bythe device C is preferably a primary control and is more rapid than that under the influence of the device C". This primary and secondary control may be effected by an arrangement similar to the one illustrated in Fig. 1a. In this manner, the devices C and C" cooperate to maintain a flow of. combustion gases through ,the furnace proportional to the master control current and, in addition, to maintain the pressure in the combustion chamber substantially constant.

The control of the feed water in this instance is modied by a device such as a thermocouple 95, responsive to the temperature of the Water in the flash tube of the boiler near the inlet but displaced therefrom suciently to register a temperature appreciably above the inlet temperature and affording an indication of the outlet temperature of the boiler, assuming a' predetermined instrument C'.

Jthermal gradient through the boiler. The electromotive force of the thermocouple is balanced against that of potentiometer 96 through a contact-making instrument 91, the contacts 98 of which control a motor-operated rheostat connected to by-pass a variable portion'of the master control current from the current balance of the Since the thermocouple 95 is placed relatively near the inlet of the boiler, it responds quickly to any change in the rate of flow of feed water, as evidenced by a change in temperature, to modify the action of the controller C' to adjust the rate of flow of feed water and maintain the temperature of the uid outlet of the boiler approximately constant.

The regulating action of the thermocouple 95 is, in turn, modied by a thermocouple-potentiometer arrangement 0|-84 similar to that of Fig. 1, which changes the setting of the potentiometer 96 in-response to changes in temperature of the steam delivered by the boiler. The thermocouple 8l operates with a considerable time-delay because of the time required for the water to pass through the tube of the boiler, which may amount to a period of several minutes. Thus, theV thermocouple 95 furnishes a rapid and approximate control of the feed water to maintain a constant output temperature, while the thermocouple 8|, with a time-delay, modifies the action of the thermocouple 95 to secure more accurate regulation of this temperature.

In some instances, it may be found that the thermal gradient through the boiler, as determined by the number and location of the turns creasing, while in others decreasing. To com-1 pensate for this vvariation in thermal gradient, the secondary control of the feed water by the thermocouple 95 may be modified as shown in` Fig. 2a. In this case, an additional load-ratio potentiometer |32 is provided having an adjustable contact |32a movable with the contact 32a. The adjustable electromotive force from this p6- tentiometer is impressed upon conductors |04, which are included in series with the circuit of the thermocouple 95 and serve `to introduce. therein an electromotive force varying with load. By a proper calibration of the potentiometer- |32, the electromotive force thereof may be made to compensate for variations in the temperature, as registered by the thermocouple 35, from that corresponding to a predetermined thermal gradient through the boiler.

In Fig. 3 is illustrated diagrammatically a circuit which may be utilized in lieu of the load responsive control of the motor-operated rheostat 25 of Fig. 1. This circuit is shown as applied to a 3-phase alternating current circuit 99, the power output of which is measured by a wattmeter |00 which is preferably of the thermoelectric type generating a thermoelectromotive force proportional to the power output of the circuit in which it is included. This electromotive force of the device |00 is balanced against the sum of the electromotive forces of a potentiometer |0| and a potentiometer |02 included in series with the lcircuit o !,the master control current. The balance of these two opposing electromotive forces is determined by a contact making instrument |03, the

master control circuit 2 I.

The circuit arrangement of Fig. 3 is operative to vary the proportionality between the power output of the circuit 99 and the master control currentlin the circuit 2| and, at the same time, to provide for a component of the master control current dependent only upon a constant adjustl able value which may be representative of the losses of the system, which are substantially independent of the load thereon. Under normal operating conditions, the action of this load control circuit is similar to that of Fig. 1. A departure of the load on the circuit |00 from that corresponding to the given value of the master control current unbalances the circuit, including the potentiometers |0I, |02 and thedevice |00,and the instrument |03 controls the motor-operated rheost at 25 to vary the master control current to restore the balance and to change the conditions of steam generation to correspond to the new load condition. In case it should be desired to change the master control current for a given load, as might be required, for example, by a change in turbine efficiency or for other change in the operating conditions of the system, the adjustable contact of the potentiometer |02 is moved, increasing or decreasing the proportion of the electromotive force of the potentiometer 02 introduced into the balancing circuit. 0n the other hand, in case the operating conditions ofthe system should change so that the heat losses of the system are changed, the constant component of the electromotive force may be adjusted by adjusting the contact 0 la of the potentiometer |0|, which varies""th'e electromotive,`Y`V

force of the potentiometer |0|. By these means the proportionality between the load upon the unit and the variable component of the master control current may be varied without varying the relative magnitude of the electromotive force representative of the constant losses of the system, while this latter quantity may be independently adjusted to take into consideration variations in operating conditions of the system.

While I have illustrated and described alternative apparatus for regulating the master control current of a combustion control system in response to several operating conditions of the sysv`tem or combinations thereof, and numerous control devices responsive to the master control current for governing the conditions of combustion in the system, it will be apparent tofthose skilled in the art that my invention is not limited to the examples specifically illustrated and described, but embodies also other combinations of the devices and apparatus to meet the requirements of a particular system, and also such other changes and modications ,as fall within the true spirit and scope of my invention.

What I claim is:

1. A combustion control system for a fluiddriven prime mover system including .a prime mover, a boiler for supplying motive fluid thereto.

and an electric generator driven thereby, comprising means for establishing a master control current, means for regulating said control current in accordance with variations in frequency of the current output of said generator, means for modifying the action of said regulating means in accordance with the electrical power output of said generator, and a plurality of control devices individually regulated by said control current for governing conditions of combustion in said boiler.

2. A combustion control system for a uuid-'- driven prime mover system including a prime mover, a boiler for supplying motive uid thereto and an electric generator driven thereby. comgenerator, relatively slow-acting means for modi-l fying the action of said regulating means in accordance with the electrical power output of said generator, and a plurality of control devices individually regulated by said control force for governing conditions of combustion in said boiler.

3. A combustion control system for a prime mover system including a prime mover, an electric generator driven thereby, and boiler means for supplying motive fluid to said prime mover; comprising means for controlling said boiler means including relatively quick-acting means responsive to the frequency of the current output of said generator and relatively slow-acting means responsive to the electrical power output thereof and acting independently of said frequency responsive means whereby the condition of combustion of said boiler means is controlled primarily to maintain constant frequency and secondarily to maintain a predetermined load characteristic.

4. A combustion control system for a fluiddriven prime mover system including a prime mover, a boiler for supplying motive fluid thereto arid an electric generator driven thereby, comprising means for establishing a master control force, means for regulating said control force including a frequency-responsive network energized from said generator, means for modifying the action of said regulating means including means responsive to the power output of said generator, and a plurality of control devices individually regulated by said control force for governing conditions of combustion in said boiler.

5. A combustion control system for a fluiddriven prime mover system including a plurality of units each consisting of a fluid-driven prime mover, a boiler for supplying motive fluid there-l to and an electric generator driven thereby, said A electric generators being connected in parallel, comprising means, for establishing master control forces individual to said units, means for coincidentally regulating said control forces in response to system frequency, means for individually modifying the action of said regulating means on said control forces in accordance with the relative power outputs of said generators, and a group of control devices cooperating with each boiler and regulated by the'control force of its respective unit for governing the conditions of combustion in said boiler.

6. A combustion control system for a fluid-driven prime mover system iraluding a'plurality of units each consisting of a. fluid-driven prime mover, a boiler for supplying motive fluid thereto and an electric generator driven thereby, said electric generators being connected in parallel, comprising means for establishing master control currents individual to said units, a frequencyresponsive network energized from said generators and means controlled thereby for coincidentally regulating said control currents, potentiometer impedances individual to said units and connected in a control circuit, means responsive to the electrical power output of each of said generators for adjusting a connection to an impedance of its 'respective unit, an instrument individual to each of said units included in said control circuit for regulating its respective master control current, and a group of control devices,

cooperating with each boiler and regulated by the control current of its respective unit for master control force, means for regulating said control force in accordance with variations in frequency of the current output of said generator, means for modifying the action of said regulating means in accordance Awith the electrical power output of said generator, a plurality of control systems energized in multiple from said control force, and a group of control devices cooperating with each of said boilers for governing conditions of combustion therein, each group of control devices being included in one of said control systems, and means for adjusting .the distribution of force between said multiple systems to effect a corresponding load distribution between said boilers.

8. A combustion control system for a prime mover system including a plurality of Huid-driven prime movers, a boiler for supplying motive iiuid thereto and a plurality of electric generators individually driven by said prime movers and connected to a common circuit, comprising means for establishing a master control force, means for regulating said control force including a frequency-responsive network energized from said generators, a plurality of control devices individually regulated by said control force for governing conditions of combustion in said boiler, and means responsive to the power outputs of said generators for adjusting the distribution of motive fluid from said boiler to said prime movers.

9. A combustion control system for a prime mover system including a plurality of units, one including a fluid-driven prime mover, a boiler for supplying motive fluid thereto and an electric generator driven thereby and another including a plurality of prime movers, a single boiler for supplying motive uid thereto and a plurality of electric generators individually driven by said prime movers, all of said electric generators being connected to a common circuit, comprising means for establishing master control forces individual to said units, means for coincidentally regulating said control forces in response to system frequency, means for individually modifying the action of saidregulating means on said control forces in accordance with the relative power outputs of the generators of said units, means responsive to the power outputs of the generators of said second-named unit for adjusting the distribution of motive fluid from its respective boiler to the several prime movers thereof, and a group of control devices cooperating with each boiler and regulated by the control force of its respective unit for governing the conditions of combustion in said boiler.

10. A combustion control system for a fluiddriven prime mover system including a prime mover, a boiler for supplying motive fluid thereto and an electric generator driven thereby, comprising means for establishing a master control current, means for regulating said control current in accordance with an operating condition of the system, a plurality of devices for controlling the supply of air, fuel, and motive fluid to said boiler, control means individual to said supply control ydevices and responsive jointly tosaid control current and to the supply of media as controlled by their respective devices, and means responsive ling the supply of air, fuel, and motive fluid tosaid boiler, control means individual to said supply control devices and responsive jointly to said control current and to the supply of media as controlled by their respective devices, and means responsive solely to the pressure within the combustion chamber of said boiler for varying the resistance to iiow through the combustion chamber of the products of combustion to maintain said pressure substantially constant.

12. A combustion control system for a fluiddriven prime mover system including a prime mover, a boiler for suppl ing motive uid thereto and an electric genera or driven thereby, comprising means for establishing a master control current, means for regulating said control current in accordance with an operating condition of the system, a plurality of devices for controlling the supply of air, fuel, and motive fluid to said boiler, control means individual to said supply controly devices and responsive jointly to said control current and to the supply of media as controlled by their respective devices, and means for maintaining substantially constant the pressure within the combustion chamber of said boiler comprising a stack damper and means responsive solely to said pressure for controlling the setting of said damper.

13. A combustion control system for a fluiddriven prime mover system including a prime mover, a boiler for supplying motive fluid thereto and an electric generator driven thereby, comprising means for regulating said control current in accordance with variations in frequency of the current output of said generator, means for modifying the action of said regulating means in accordance with the electrical power output of said generator, and a plurality of devices for controlling the supply of air, fuel, and motive uld to. said boiler, and control means individual to said supply control devices and responsive jointly to said control current and to the supply of media as controlled by their respective devices.

14. A combustion control system for a fluiddriven prime mover system including a prime4 mover, a boiler for supplying motive fluid thereto and an electric generator driven thereby, comprising means for establishing a master control force, means for regulating said cont-rol force in accordance with the electrical power output of said generator, a plurality of -control devices individually regulated by said control force for governing conditions of combustion in said boiler, and means responsive to the supply of motive fluid to said boiler for modifying the action of said regulating means on said control force.

15. A combustion control system for a duiddriven prime mover system including a prime mover, a boiler for supplying motive uid theretoand an electric generator driven thereby, comprising means for establishing a master control force,'means for regulating said control force in accordance with the electrical power output of said generator, a plurality of control devices indivldually regulated by said controlforce 'for governing conditions of combustion in said boiler, means responsive solely to the electrical power output of said generator -for controlling the supply of feed water to said boiler, and means responsive to the supply of feed .water to said boiler for modifying the action of said regulating means on saidv control force.

16. A combustion control system for a lluiddriven prime mover system including a prime mover, a. boiler for supplying motive fluid thereto and an electric generator driven thereby, comprising means for establishing a master control current, means for regulating said current in accordance with an operating condition of the system, a plurality of devices for controlling the llow of combustion gases through said boiler and the supply of fuel and motive uid thereto, control means individual to said devices and responsive jointly to said control 'current and the factors controlled by their respective devices, a device for controlling the-supply of air to said boiler, and control means cooperating with said last-named device responsive jointly to the pressure in the combustion chamber of the boiler and to the control means associated with the device for controlling the flow of combustion gases.

17. A combustion control system for a fluiddriven prime mover system including a prime mover, a flash tube boiler for supplying motive uid thereto and an electric generator driven thereby, comprising means for establishing a master control force, means for regulating said force in accordance with an operating condition of the system, a plurality of devices for controlling the iiow of combustion gases through said boiler and the supply of fuel thereto, control means individual to said devices and responsive jointly to said control force and the factors controlled by their respective devices, means for regulating the supply of motive fluid directly in accordance with said operating condition of the system, means responsive to the temperature within said boiler near the inlet thereof for modifying the action of the control means of the motive fluid supply control device, and means responsive to the load on said generator for modifying the action of the temperature responsive means to compensate for changes in thermal gradient through said boiler with changes in load.

18. A combustion control system for a fluiddriven prime mover system including a prime mover, a flash tube boiler for supplying motiveuid thereto and an electric generator driven thereby, comprising means for establishing a master control force, means for regulating said force in accordance with an `operating condition of the system, a plurality of devices for controlling the ilow of combustion gases through said boiler and the supply oi.' fuel thereto, control means individual to said devices and responsive jointly to said control force and the factors controlled by their respective devices, means for regulating the supply of motive iluid directly in accordance with said operating condition of the system, a thermocouple disposed in said boiler near the inlet thereof and connected to modify the action of the control means of the motive uid supply control device to maintain the temperature of the iluid output of said boiler approximately constant, and means for introducing into the circuit of said thermocouple an electromotive force varying with the load on said'generator to compensate for changes in thermal gradient through said boiler with changes in load.

19. A combustion control system for a uiddriven prime mover system including a prime mover, a flash tube boiler for supplying motive fluid thereto and an electric generator driven thereby, comprising means for establishing a master control force, means for regulating said force in accordance with an operating condition of the system, a plurality of devices for controlling the iioW of combustion gases through said boiler and the supply of fuel thereto, control means individual to said devices and responsive jointly to said control force and the factors controlled by their respective devices, means for regulating the supply of motive fluid directly in accordance with said operating condition of the system, a thermocouple disposed in said boiler near the inlet thereof and operating quickly to modify the action of the control means of the motive fluid supply device to maintain the temperature of the fluid output of said boiler approximately constant, a thermocouple disposed in the fluid outlet of said boiler and operating Vwith a time delay to modify the action of said first thermocouple to maintain more accurately the temperature of the fluid output of said boiler, and means for introducing into the circuit of said first thermocouple an electromotive force varying with the load on said generator to compensate for changes in thermal gradient through said boiler with changes in load.

20. A combustion control system for a fluiddriven prime mover system including a prime mover, a boiler for supplying motive fluid thereto and an electric generator driven thereby, comprising means for establishing a master control current, means for regulating said current in accordance with an operating condition of the system, a plurality of devices for controlling the flow of combustion gases through said boiler and the supply of fuel thereto, control means individual to said devices and responsive jointly to said control current and the factors controlled by their respective devices, means for regulating the supply of motive fluid directly in accordance o with said operating condition of the system, means responsive to the temperature Within said boiler near the inlet thereof for by-passing a variable portion of said control current from the control means of the motive fluid supply control device, and means responsive solely to the temperature of the fluid output of said boiler for modifying vthe action of said last-named means.

21. In a combustion control system, means for establishing a master control current for governing conditions of combustion, means for producing an effect varying with an operating condition of said system, means for producing an effect varying with said control current, means for producing an adjustable constant effect, means for regulating said control current to maintain the first of said effects proportional to the sum of the other two, and means for varying the factor of proportionality and at the same time maintaining the relative magnitude of said constant effect.

22. In a combustion control system. means for establishing a. master control current for governing conditions of combustion, means for producing an electrical effect proportional to an operating condition of said system, means for producing an electrical effect constant in magnitude, means for deriving an electrical eect proportional to said control current, means controlled by said electrical effects for regulating said control current to balance the effect derived from said operating condition and the sum of the other two effects, and means for independently varying said last-named two effects.

23. In a combustion control system, means for establishing a master control current for governing conditions of combustion, means for producing an electromotive force proportional to the electrical power output of said generator, a potentiometer impedance energized from a source of constant electromotive force, a second potentiometer impedance energized by said control current, a circuit including an electroresponsive device for comparing said first electromotive force with the sum of those across said potentiometer impedances, means including said electroresponsive device for regulating said control current to balance said circuit, means for independently adjusting the settings of said potentiometer impedances, and means for adjusting the value of said constant electromotive force.

24. A system comprising a prime mover, an alternator driven thereby, a boiler for supplying motive fluid to said prime mover, means for producing a control force, means responsive to the frequency of the current generated by said alternator for regulating said control force, and a plurality of control devices regulated by said control force for governing conditions of combustion in said boiler.

25. A system comprising a prime mover, an alternator driven thereby, a boiler for supplying motive fluid to said prime mover, means for producing a control force, means responsive to the frequency of current generated by said alternator for regulating said control force, means responsive to the'output of said alternator for modifying said control force, and a plurality of control devices egulated by said control force for governing conditions of combustion in said boiler.

26. An electric power system comprising a] generator, a prime mover therefor, boiler means for supplying motive fluid to said prime mover, means for producing an effect varying as a function of the system load, means for producing an effect varying as a function of the generator output, and means jointly responsive to said effects for'varying the rateof production of motive fluid by said boiler means.

27. An electric power system supplied from generating units each comprising a generator, a prime mover therefor, and boiler means for supplying motive uid to the prime mover, separate means for individually controlling the rate of production of motive fluid by the individual boiler means, means responsive to system load for effecting operation of said control means, and means responsive to the outputs of said generators for effecting operation of said control means to effect predetermined division of load between said units.

28. An `electric power system supplied from generating units each comprising a generator, a prime mover therefor, and boiler means for supplying motive uid to the prime mover, means responsive to the outputs of said generators, and means controlled by said responsive means individually to control the rate of production of motive fluid by said individual boiler means to accord with predetermined division of load between said generators.

29. A system comprising a generator, aprime mover therefor, boiler means for supplying motive fluid to the prime mover, means producing an eifect varying as a function of the output of said generator, means producing a standard effect, and means jointly responsive to saidv effects for controlling the rate of production of motive iiuid by said boiler means to maintain a predetermined between the outputs of the alternators associated relation of the magnitudes of said effects."

30. An electric power system supplied from generators having individual prime movers and a common boiler for supplying motive iiuid to said prime movers, means responsive to the system demand for changing the rate of production of motive iiuid by said boiler, means producing effects each varying as a function of the output of one of the generators, and means responsive to said eiects for varying the distribution of motive uid from said boiler to said prime movers to eect predetermined division of load between said generators.

31. An electric power system comprising boilers, .one or more prime moverslsupplied with motive iluid from each of said boilers and individual thereto, alternators individually driven by said prime movers, means responsive to changesv in system frequency for similarly varying the rate of production of motive uld by said boilers, means producing eiects each varying as a function of the output of one of said alternators, and

varying the rate of production of motive uid by said boilers to maintain a predetermined relation with the diierent boilers. 32. An electric power system comprising boilers, one or more prime movers supplied with motive uid from each of said boilers and individual thereto, alternators individually driven by said prime movers, means responsive to changes in system frequency for similarly varying the rate of production of motive iiuid by said boilers,

of motive uid to prime movers supplied from a 20 common boiler to maintain a predetermined relation between the outputs of alternators associated with the same boiler.

EDWARD S. BRISTOL.

25 means responsive to said eiects for individually 25 CERTIFICATE 0F CORRECTION.

Patent No.v 2,053,061. September l, 1936.

EDWARD S. BRISTOL.

It is hereby certified that error appears in the print-ed specification or the above numbered patent requiring correction -as follows: Page 2, second column, line 46, for the syllable and words "tudes, as determined by the calibration of the" read of direct current through either the contacts 30a; page 7, first column, line 14, claim 3, strike out the semicolon after "mover" and that the said Letters Patent should be read with these correo# tions therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 16th day of March, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

